Method for producing oxide magnetic material based on permanent magnet

Abstract

The present invention provides a method for manufacturing a permanent magnet based on oxide magnetic material, comprising a binder addition step for adding a binder to raw material powder containing oxide magnetic materials for mixing; a water content adjustment step for adjusting the water content of a molding mixture containing the raw material powder and the binder; an in-magnetic-field dry molding step for loading the molding mixture with adjusted water content into a mold and pressing it in a magnetic field applied while aligning the directions of easy magnetization of oxide magnetic material powder particles; and a sintering step for sintering the molded body; wherein the binder in the binder addition step is a wax based on fatty acid ester, and wherein the molding mixture charged into the mold in the in-magnetic-field dry molding step contains aggregates, in which the percentage of existence of aggregates in size of 500 μm or more is 0.01 to 0.80 wt %, thus obtaining the permanent magnet based on oxide magnetic material with excellent magnetic properties while cutting down on costs.

What is claimed is:  
     
         1 . A method for manufacturing a permanent magnet based on oxide magnetic material, comprising: 
 a binder addition step for adding a binder to raw material powder containing oxide magnetic materials for mixing;    a water content adjustment step for adjusting a water content of a molding mixture containing the raw material powder and the binder;    an in-magnetic-field dry molding step for loading the molding mixture with adjusted water content into a mold and pressing it in a magnetic field applied while aligning the directions of easy magnetization of oxide magnetic material powder particles; and    a sintering step for sintering the molded body; wherein the binder in the binder addition step is a wax based on fatty acid ester, and    wherein the molding mixture charged into the mold in the in-magnetic-field dry molding step contains aggregates, in which the percentage of existence of aggregates in size of 500 μm or more is 0.01 to 0.80 wt %.    
     
     
         2 . The method for manufacturing a permanent magnet based on oxide magnetic material as defined in  claim 1 , wherein the water content of the mixture in the water content adjustment step is 0.20 to 0.80 wt %.  
     
     
         3 . The method for manufacturing a permanent magnet based on oxide magnetic material as defined in  claim 1 , wherein the wax based on the fatty acid ester is a vegetable wax.  
     
     
         4 . The method for manufacturing a permanent magnet based on oxide magnetic material as defined in  claim 1 , wherein the raw material powder of the oxide magnetic materials is prepared by compounding and mixing raw oxide materials, and then calcining the raw oxide materials and thereafter crushing them.  
     
     
         5 . The method for manufacturing a permanent magnet based on oxide magnetic material as defined in  claim 1 , wherein the water content adjustment step includes adjusting the water content of the mixture while controlling the humidity.  
     
     
         6 . The method for manufacturing a permanent magnet based on oxide magnetic material as defined in  claim 1 , wherein the binder content of the molding mixture is 0.2 to 1.5 wt %.  
     
     
         7 . The method for manufacturing a permanent magnet based on oxide magnetic material defined in  claim 1 , further comprising a crushing step which follows the water content adjustment step, for crushing aggregates in the molding mixture.  
     
     
         8 . The method for manufacturing a permanent magnet based on oxide magnetic material as defined in  claim 7 , wherein the water content of the mixture is 0.20 to 0.80 wt % at the completion of the crushing step.